The present invention relates generally to microsurgical instruments and more specifically, but not by way of limitation, to microsurgical instruments suitable for the implantation of intracorneal optical lenses (ICOLs).
The human eye in its simplest terms functions to provide vision by transmitting light through a clear outer portion called the cornea, and focusing the image by way of a crystalline lens onto a retina. The quality of the focused image depends on many factors including the size and shape of the eye, and the transparency of the cornea and the lens.
The optical power of the eye is determined by the optical power of the cornea and the crystalline lens. In the normal, healthy eye, sharp images are formed on the retina (emmetropia). In many eyes, images are either formed in front of the retina because the eye is abnormally long (axial myopia), or formed in back of the retina because the eye is abnormally short (axial hyperopia). The cornea also may be asymmetric or toric, resulting in an uncompensated cylindrical refractive error referred to as corneal astigmatism. In addition, due to age-related reduction in lens accommodation, the eye may become presbyopic resulting in the need for a bifocal or multifocal correction device.
In the past, axial myopia, axial hyperopia and corneal astigmatism generally have been corrected by spectacles or contact lenses, but there are several refractive surgical procedures that have been investigated and used since 1949. Barraquer investigated a procedure called keratomileusis that reshaped the cornea using a microkeratome and a cryolathe. This procedure was never widely accepted by surgeons. Another procedure that has been used is radial and/or transverse incisional keratotomy (RK or AK, respectively). Photoablative lasers have also been used to reshape the surface of the cornea (photorefractive keratectomy or PRK) or for mid-stromal photoablation (Laser-Assisted In Situ Keratomileusis or LASIK). All of these refractive surgical procedures cause an irreversible modification to the shape of the cornea in order to effect refractive changes, and if the correct refraction is not achieved by the first procedure, a second procedure or enhancement must be performed. Additionally, the long-term stability of the correction is variable because of the variability of the biological wound healing response between patients.
Permanent intracorneal implants made from synthetic materials are also known for the correction of corneal refractive errors. Such implants may be generally classified into two categories.
One category is intracomeal implants that have little or no refractive power themselves, but change the refractive power of the cornea by modifying the shape of the anterior surface of the cornea. U.S. Pat. No. 5,123,921 (Werblin, et al.); U.S. Pat. Nos. 5,505,722, 5,466,260, 5,405,384, 5,323,788, 5,318,047, 5,312,424, 5,300,118, 5,188,125, 4,766,895, 4,671,276 and 4,452,235 owned by Keravision and directed to intrastromal ring devices; and U.S. Pat. No. 5,090,955 (Simon), U.S. Pat. No. 5,372,580 (Simon, et al.), and WIPO Publication No. WO 96/06584 directed to Gel Injection Adjustable Keratoplasty (GLAK) all disclose examples of this category of implant.
A second category is intracomeal implants having their own refractive power. U.S. Pat. No. 4,607,617 (Choyce); U.S. Pat. No. 4,624,669 (Grendahl); U.S. Pat. No. 5,628,794 (Lindstrom); and U.S. Pat. Nos. 5,196,026 and 5,336,261 (Barrett, et al.) provide several examples of this category. In addition, U.S. patent application Ser. No. 08/908,230 filed Aug. 7, 1997 entitled xe2x80x9cIntracomeal Diffractive Lensxe2x80x9d, which is incorporated herein in its entirety by reference, discloses an example of an ICOL that has both refractive and diffractive powers.
Microsurgical instruments used for the implantation of such intracomeal implants have also been developed. For example, WIPO Publication No. WO 99/30645 owned by Keravision discloses a variety of instruments for creating grooves in the stromal tissue for implanting a ring-shaped intracomeal implant or a pocket for implanting ICOLs. These tools may be used manually, but are preferably used in cooperation with a vacuum centering device. Another instrument used for creating an intracomeal pocket for implanting an ICOL is described in U.S. patent application Ser. No. 09/434,912 filed Nov. 5, 1999 entitled xe2x80x9cLamellar Dissecting Instrumentxe2x80x9d, which is incorporated herein in its entirety by reference. However, after formation of an intracorneal pocket, an ICOL is typically positioned within the intracorneal pocket using conventional forceps, such as intraocular lens folding forceps. With conventional forceps, a surgeon must spend several minutes xe2x80x9cspreading outxe2x80x9d or flattening the ICOL within the intracorneal pocket and manipulating it into proper position within the pocket.
Accordingly, a need exists for a microsurgical instrument that more effectively positions an ICOL within an intracorneal pocket. The instrument should be easy for the surgeon to use, should maximize patient safety, and should be economically feasible.
One aspect of the present invention is an instrument for positioning an intracorneal optical lens within an intracorneal pocket. The instrument generally includes a handle and a cannula associated with and having a distal portion extending from the handle. The cannula is for fluidly coupling to a vacuum source in a first mode of operation and to a reservoir of surgical fluid in a second mode of operation. The distal portion of the cannula is for receiving the lens in a folded position around the distal portion. The distal portion has an aperture for providing vacuum to hold the lens in the folded position in the first mode of operation and for ejecting surgical fluid in an outward direction from the distal portion to help unfold the lens in the second mode of operation.